A specific inhibitor of interleukin-1alpha (IL-1alpha) has been partially purified from pooled synovial fluids of patients with rheumatoid arthritis. This synovial fluid inhibitor of IL-1alpha (SFIalpha) is distinct from previously described IL-1 inhibitors because it has no effect on in vitro activities of IL-1beta. SFIalpha inhibits the specific binding of radiolabeled IL-1alpha to cells bearing IL-1 receptors, but has no effect on the binding of IL-1beta. Thus, it is different from a recently described IL-1 receptor antagonist, inhibits binding and activities of both forms of IL-1. Preliminary results suggest that SFIalpha acts by specifically binding IL-1alpha and preventing receptor occupancy. The first aim of this proposal is to purify SFIalpha using classical biochemical techniques. SFIalpha will be characterized with respect to N-terminal amino acid sequence, molecular weight, and role of carbohydrate residues in activity. The cellular source of SFIalpha will be identified by immunohistochemical staining of synovial tissues with monoclonal anti-SFIalpha, and by in vitro assays of cells from synovial fluid and other sources for biological activity. A cDNA clone will then be produced using either oligonucleotide probes, antibody probes, or expression cloning. The long-term goals of this research are to elucidate the cDNA sequence for SFIalpha and to produce recombinant inhibitor protein, which could have important applications in the treatment of rheumatoid arthritis and other chronic inflammatory diseases. The availability of both monoclonal antibody and recombinant IL-1alpha inhibitor protein will allow detailed studies of the regulation of IL-1 activity.